DEV: Remove `build_test_topic` task (#15068)

I don't think anyone is using it anymore

lib/tasks/build_test_topic.rake

@@ -1,51 +0,0 @@
-# frozen_string_literal: true
-
-# Build a test topic full of links to test our replaceState/pushState functionality.
-
-desc 'create pushstate/replacestate test topic'
-task 'build_test_topic' => :environment do
-  puts 'Creating topic'
-
-  # Acceptable options:
-  #
-  #   raw                     - raw text of post
-  #   image_sizes             - We can pass a list of the sizes of images in the post as a shortcut.
-  #
-  #   When replying to a topic:
-  #     topic_id              - topic we're replying to
-  #     reply_to_post_number  - post number we're replying to
-  #
-  #   When creating a topic:
-  #     title                 - New topic title
-  #     archetype             - Topic archetype
-  #     category              - Category to assign to topic
-  #     target_usernames      - comma delimited list of usernames for membership (private message)
-  #     meta_data             - Topic meta data hash
-  evil_trout = User.find_by_username('EvilTrout')
-
-  first_post = PostCreator.new(evil_trout, raw: "This is the original post.", title: "pushState/replaceState test topic").create
-  topic = first_post.topic
-
-  topic_url = "#{Discourse.base_url}/t/#{Slug.for(topic.title)}/#{topic.id}"
-
-  99.times do |i|
-    post_number = (i + 2)
-
-    links = []
-    [-30, -10, 10, 30].each do |offset|
-      where = (post_number + offset)
-      if where >= (1) && where <= (100)
-        links << "Link to ##{where}: #{topic_url}/#{where}"
-      end
-    end
-
-    raw = <<eos
-This is post ##{post_number}.
-
-#{links.join("\n")}
-eos
-
-    PostCreator.new(evil_trout, raw: raw, topic_id: topic.id).create
-  end
-
-end